1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly, to a liquid crystal panel having a specific material for the gap between a display panel and a back panel such as a TFT substrate or the like.
2. Description of the Prior Art
Recently, liquid crystal panels have been generally popular because they can be manufactured in a thin and light structure having low power consumption, a large display screen and uniform and excellent image quality. Each of these liquid crystal panels is constructed by two substrates which are spaced from each other at a predetermined interval, and liquid filled in the gap between the pair of substrates. It is preferable to keep the gap between the two substrates uniform and suppress gap unevenness in order to obtain liquid crystal display panels having excellent display quality. The gap unevenness occurs due to partial (local) deformation of the substrate caused by press or due to distortion of the substrates caused by expansion of the liquid crystal at high temperatures. Therefore, in order to keep the gap uniform, there has been generally used a method of scattering spherical gap holding materials in the gap between the substrates.
With respect to a direct view type liquid crystal display panel, a liquid crystal display panel for use in a projection type projector for displaying an image display on a large-scale screen through an enlarging lens is particularly required to be compact in size and highly fine in quality. However, it has such a disadvantage that the gap control materials scattered in a display portion area are imaged at the projection time to lower the display quality, or such a disadvantage that irregularity of colors occurs due to dispersion of the panel gap when displays of RGB are combined in a three-plate projection type projector.
In order to solve these disadvantages, it has been required to implement a spacer less panel in which no gap control material is scattered in the display area, and also implement highly-precise gap uniformity.
In the small type liquid crystal display panel for use in the projection type projector as described above, for the purpose of implementing the spacer less design, there is known a method of dispersing a gap control material in only a seal pattern portion (the outer peripheral portion of the panel) to control the panel gap.
However, the method of controlling the gap by only the sealing portion has the following disadvantages: In a press step for panel attachment, the gap control material mixed in the sealing material is excessively pressed in, so that it breaks the wiring pattern under the seal pattern, or it causes the wires to be short-circuited to each other if the wiring pattern under the seal pattern is designed in a multilayer wiring structure. Further, a large dispersion in gap control occurs due to warp/waviness of the substrates or steps of the back film or wires.
Techniques to solve the above disadvantages disclosed in Japanese Laid-open Patent Publication No. Hei-03-287127 (hereinafter referred to as xe2x80x9cfirst publicationxe2x80x9d) and Japanese Laid-open Patent Publication No. Sho-63-155128 (hereinafter referred to as xe2x80x9csecond publicationxe2x80x9d) are known as prior arts showing conventional liquid crystal panels.
The first publication discloses the technique that the particle diameter of a first spacer is larger than that of a second spacer mixed in a sealing material on the periphery of the panel and the ration of the first and second spacers is specified to obtain a high-contrast display. According to the first publication, as shown in FIG. 1, black spherical resin fine particles having a compressive elastic coefficient of 9.8xc3x97108 to 4.9xc3x97109 Pa (100 to 500 kgf/mm2) are used as first spacer 23 for controlling the gap, inorganic second spacer 24 is mixed in the sealing material 25, the particle diameter of the first spacer 23 is set to be larger than that of the second spacer 24 and the mixing ratio of the first and second spacers is set in the range of 1:0.98 to 1:0.84. In this case, a pair of substrates 21 and 22 are pressed under predetermined pressure and fixed to each other with the sealing material 25. At this time, the substrates 21 and 22 are bent and the first spacer 23 suffers pressure deformation, and thus when the load is subsequently removed, the substrates 21, 22 and the spacer 23 are kept into close contact with each other by the repulsive force based on the elastic force of the spacer 23. Accordingly, the gap accuracy between the substrates is dependent on the unevenness of the surfaces of the substrates and thus the uniform gap can be formed, thereby enhancing the display contrast.
The second publication discloses the technique that a mixture of first soft particle having high elastic coefficient and second hard particle having low elastic coefficient is used as a spacer for a liquid crystal display device, so that uniform optical characteristics can be obtained over the overall surface without color irregularity and there is no limitation in usable temperature range. According to the second publication, in a liquid crystal display device, light-transmissible electrodes 32, 37 and oriented films 33, 38 are formed on light-transmissible substrates 31, 36, and the oriented films 33, 38 are disposed so as to confront each other slightly away from each other as shown in FIG. 2. Further, a sealing material 34 of epoxy resin film is formed on the peripheral portion of the liquid crystal display device so that thin gap 39 is formed between the two oriented films 33 and 38, and spacer 35 is scattered in the gap 39. The spacer 35 is made of the mixture of first soft particles having high elastic coefficient and second particles which are mixed by 10% or less of the particle amount of the first particles and is harder and lower in elastic coefficient than the first particles. Consequently, the cell gap length can be accurately controlled, uniform optical characteristics and no irregularity of colors can be obtained over the overall surface, and the usable temperature range can be widened.
However, the above conventional prior art has the following disadvantages:
A first disadvantage resides in that any of the above-described conventional techniques suffer degradation in pixel-based display quality because the gap control material is scattered in the display pixel portion of the liquid crystal panel for the following reason. A liquid crystal display panel for use in a projection type projector is required to be designed in a compact and highly fine structure, and thus the occupational area rate of the gap control material itself over one pixel approaches to 20%, resulting in dispersion of the display state between a pixel on which the gap control material exists and a pixel on which no gap control material exists. Further, in consideration of the shape of the gap control material, the gap control material existing in the pixel portion serves as a factor to disturb the orientation of the liquid crystal layer or scatter light incident to the pixel portion due to its optical characteristic.
A second disadvantage resides in that as described with reference to the first publication, the gap control material mixed in the sealing material is excessively pressed in the press step for the panel attachment to break the wiring pattern under the seal pattern, and if the wiring pattern under the seal pattern is designed in a multi layered wiring structure, the wires are short-circuited. This is because use of hard materials as the gap control material is more effective to enhance the uniformity of the gap, however, the hard materials are more liable to crush the wires.
An object of the present invention is to provide a liquid crystal display panel in which the panel gap is controlled, the process failure occurring in a seal press process can be reduced and the gap controllability can be enhanced by dispersing two kinds of gap control materials having different physical property values from each other into a sealing material on the outer periphery of the panel.
In order to attain the above object, according to the present invention, a liquid crystal display panel comprising first and second substrates which are spaced from each other at a predetermined gap, and a liquid crystal sealed in the gap between the pair of first and second substrates, which comprises a seal material which is applied on the outer periphery of the first and second substrates, and two kinds of gap control materials dispersed in the seal material.
In the above liquid crystal display panel, the two kinds of gap control materials consist of a first gap control material of particles softer than an insulating film (back film) and wires disposed on the first substrate, and a second gap control material of particles harder than the insulating film (back film) and wires disposed on the first substrate, and a maximum particle diameter in consideration of the standard deviation of the first gap control material is set to be larger than a maximum particle diameter in consideration of the standard deviation of the second gap control material.
In the above liquid crystal display panel, the relationship between an average (x1) and standard deviation ("sgr"1) of the particle diameter of the first gap control material and an average (x2) and standard deviation ("sgr"2) of the particle diameter of the second gap control material substantially satisfies the following formula:
(x1+3xc3x97"sgr"1)xe2x88x92(x2+3xc3x97"sgr"2)=xcex94h
wherein xcex94h represents a differential height of said insulating film formed by said wires located under said seal material.
In the above liquid crystal display panel, the standard deviation of the second gap control material is set to the same level as or smaller level than the standard deviation of the first gap control material.
In the above liquid crystal display panel, the compressive elastic coefficient of the first gap control material is set in the range of 9.8xc3x97108 to 4.9xc3x97109 Pa (Pascal).
In the above liquid crystal display panel, the compressive elastic coefficient of the second gap control material is set in the range of 4.9xc3x97109 to 2.45xc3x971011 Pa (Pascal).
In the above liquid crystal display panel, the mixing rate of the second gap control material to the first gap control material is set in the range of about 0.1 time to about 2 times.